A storage system is a computer that provides storage service relating to the organization of information on writable persistent storage devices, such as memories, tapes or disks. The storage system may be deployed within a storage area network (SAN) or a network attached storage (NAS) environment. When used within a NAS environment, the storage system may be embodied as a file server including an operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on, e.g., the disks. Each “on-disk” file may be implemented as a set of data structures, e.g., disk blocks, configured to store information, such as the actual data for the file. A directory, on the other hand, may be implemented as a specially formatted file in which information about other files and directories are stored.
The file server, or filer, may be further configured to operate according to a client/server model of information delivery to thereby allow many client systems (clients) to access shared resources, such as files, stored on the filer. Sharing of files is a hallmark of a NAS system, which is enabled because of semantic level of access to files and file systems. Storage of information on a NAS system is typically deployed over a computer network comprising a geographically distributed collection of interconnected communication links, such as Ethernet, that allow clients to remotely access the information (files) on the filer. The clients typically communicate with the filer by exchanging discrete frames or packets of data according to pre-defined protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP).
In the client/server model, the client may comprise an application executing on a computer that “connects” to the filer over a computer network, such as a point-to-point link, shared local area network, wide area network or virtual private network implemented over a public network, such as the Internet. NAS systems generally utilize file-based access protocols; therefore, each client may request the services of the filer by issuing file system protocol messages (in the form of packets) to the file system over the network. By supporting a plurality of file system protocols, such as the conventional Common Internet File System (CIFS), the Network File System (NFS) and the Direct Access File System (DAFS) protocols, the utility of the filer may be enhanced for networking clients.
A SAN is a high-speed network that enables establishment of direct connections between a storage system and its storage devices. The SAN may thus be viewed as an extension to a storage bus and, as such, an operating system of the storage system enables access to stored information using block-based access protocols over the “extended bus”. In this context, the extended bus is typically embodied as Fibre Channel (FC) or Ethernet media (i.e., network) adapted to operate with block access protocols, such as Small Computer Systems Interface (SCSI) protocol encapsulation over FC or TCP/IP/Ethernet.
A SAN arrangement or deployment allows decoupling of storage from the storage system, such as an application server, and placing of that storage on a network. However, the SAN storage system typically manages specifically assigned storage resources. Although storage can be grouped (or pooled) into zones (e.g., through conventional logical unit number or “lun” zoning, masking and management techniques), the storage devices are still pre-assigned by a user, e.g., a system administrator, to the storage system.
Storage virtualization generally involves the pooling of storage resources from multiple storage devices, such as physical disks, typically across a network by one or more storage systems to create a “user-defined volume”. The term “volume” as conventionally used in a SAN environment implies a storage entity that is constructed (by a system administrator) by specifying physical disks and extents within those disks via operations that combine those extents/disks into a user-defined volume storage entity. An extent is a set of contiguously addressed blocks (or “slices”) of storage within the specified physical disks. Such construction can occur on either the storage device or application server. Storage virtualization is often used as part of a SAN deployment, wherein the user-defined volume appears as a single storage entity to the operating system, regardless of the types of storage devices pooled. Virtualization thus separates the representation of storage to the operating system from the actual physical storage connected over the network.
Storage virtualization has many interpretations, including decoupling of physical disk size limitations and underlying physical structure from a user-defined volume corresponding to a disk or lun. Virtualization may also refer to management of luns, including defining underlying reliability guarantees of the storage. Commonly, this aspect of virtualization is accomplished through explicit mirroring or Redundant Array of Independent (or Inexpensive) Disks (RAID) protection levels to a lun that is formed from the storage pool. That is, the system administrator explicitly defines the underlying reliability guarantees of the constructed user-defined volume. It can be appreciated that this administrative procedure is complex, time consuming and, therefore, costly.
Virtualization may further denote the ability to modify an existing configuration of a lun (e.g., to increase its size) along with the performance characteristics of the lun. However, conventional physical disks and strategies that explicitly construct larger units of storage for use by clients may suffer performance limitations. For example, bandwidth to a user-defined volume constructed through explicit aggregation of a number of disks and/or “slices” (extents) of those disks may be limited by physical constraints of the underlying properties of the constructed volume.
Therefore, the conventional notion of storage virtualization involves presenting a view of storage (i.e., a user-defined volume) to a client wherein the volume is formed from extents of various disks accessible to the client that are selected by a user or system administrator. The selection process performed by the administrator generally includes (i) choosing the various extents from the disks associated with the storage accessible to the client, (ii) applying underlying reliability guarantees (such as RAID or mirroring) to those extents to ensure the reliability of the volume, and (iii) presenting those reliable extents as a single storage entity (e.g., disk or lun) to a client. The present invention is directed to efficiently carrying out a storage virtualization selection process on a storage system.